The present invention relates to a process for preparing a Ti (III) coordination complex by the reduction of a Ti (IV) salt, such as a halide (preferably a chloride or bromide) which comprises reducing substantially all of the Ti (IV) salt with a metal powder that forms a soluble metal salt by-product.
The present invention, in a preferred embodiment, describes a process for the preparation of low Al and substantially Al-free TiCl.sub.3. Such compounds are useful as polymerization catalyst precursors and as reducing agents in organic synthesis.
Recently it was reported (U.S. Pat. No. 5,264,590) that low-Al stoichiometric TiCl.sub.3 (ether) complexes can be prepared by reacting organoaluminum compounds with titanium tetrachloride in certain ethers, such as tetrahydrofuran (THF) to form TiCl.sub.3 (ether) products. For example, the precipitated TiCl.sub.3 (THF).sub.3 product can then be separated from the soluble AlCl.sub.3 (THF) complex. However, caution must be exercised in performing such a reaction. Addition of the alkylaluminum reagent to the ether mixture releases heat, so that a low temperature and a slow addition rate are required. Secondly, the alkylaluminum reagent is pyrophoric. Lastly, certain alkyl aluminum compounds may reduce the TiCl.sub.4 into the undesirable TiCl.sub.2 by-product.
An alternative process for preparing TiCl.sub.3 (THF).sub.3 was reported in 1975 (S. Tyrlik et al., J. Organomet. Chem., 1975, 93, 353-362). In this process TiCl.sub.4 reacts at room temperature with Al ribbon in THF solvent to form TiCl.sub.3 (THF).sub.3 : ##STR1## This process is convenient for lab-scale preparations, but physically separating the TiCl.sub.3 (THF).sub.3 from the Al ribbon may prove to be difficult on large-scale.